Power supply circuit

ABSTRACT

A power supply circuit for a graphic card on a motherboard includes first to fourth electrical switches. The first electrical switch is connected to the motherboard to receive a power good signal from the motherboard. The second electrical switch is connected between the first electrical switch and each of the third and fourth electrical switches. The third and fourth electrical switches provide power to the graphic card. The first electrical switch is turned on or off according to the voltage of the power good signal. The second electrical switch is turned on or off by the first electrical switch, so as to selectively control one of the third and fourth electrical switches turn on to output power to the graphic card.

BACKGROUND

1. Technical Field

The present disclosure relates to power supply circuits, and moreparticularly to a power supply circuit for graphic cards.

2. Description of Related Art

Commonly, although graphic cards within a computer system are idle whenthe computer system is on standby, a power supply continues to providepower to the graphic cards to allow the graphic cards to quickly respondonce the computer wakes.

The voltage of the power supply is usually 3.3 volts (V). The circuitoutputting a 3.3V voltage is complicated and costly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an exemplary embodiment of a power supplycircuit connected to a 3.3 volt (V) standby power supply.

FIG. 2 is a circuit diagram showing generation of the 3.3V standby powersupply of FIG. 1, in accordance with an embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary embodiment of a power supply circuitproviding power to a graphic card 12 of a motherboard 10 of a computerincludes three n-channel enhanced metal-oxide-semiconductor field-effecttransistors (MOSFETs) Q1, Q2, and Q4, a p-channel enhanced MOSFET Q3,two resistors R1 and R2, and a capacitor C1.

A gate of the MOSFET Q1 receives a power good signal PWR_OK from themotherboard 10, a source of the MOSFET Q1 is grounded, a drain of theMOSFET Q1 is connected to a 3.3V standby power supply 3.3V_SB via theresistor R1. A gate of the MOSFET Q2 is connected to the drain of theMOSFET Q1, a source of the MOSFET Q2 is grounded, and a drain of theMOSFET Q2 is connected to a 12V first power supply VDD via the resistorR2. A gate of the MOSFET Q3 and a gate of MOSFET Q4 are both connectedto the drain of the MOSFET Q2. A drain of the MOSFET Q3 is connected tothe standby power supply 3.3V_SB. A drain of the MOSFET Q4 is connectedto a second power supply VCC. A source of the MOSFET Q3 and a source ofthe MOSFET Q4 are connected to the graphic card 12 and connected to afirst terminal of the capacitor C1. A second terminal of the capacitorC1 is grounded.

Commonly, the motherboard 10 includes several power supplies, whosestandard voltage values are respectively 12V, 5V, 3.3V, and so on. Onlywhen all the voltages of the power supplies respectively achieve thestandard voltages does the power good signal PWR_OK indicate highvoltage level, and the computer is operating normally, with voltagevalues of the first and second power supply VDD and VCC respectively 12Vand 3.3V. When the power good signal PWR_OK is at low voltage level, thevoltages output by the power supplies of the motherboard 10 are notstable, while the standby power supply 3.3V_SB outputs a stable 3.3Vvoltage all the time.

The MOSFETs Q3 and Q4 may be integrated in a chip, such as an FDS4501Hchip. In other embodiments, the MOSFETs Q1-Q4 may be replaced of othertypes of electrical switches.

Referring to FIG. 2, the standby power supply 3.3V_SB is converted by astandby power supply 5V_SB of the motherboard 10 through a voltageconverting circuit 20. The voltage converting circuit 20 includes tworesistors R3 and R4, two capacitors C2 and C3, and a voltage regulator20. The voltage regulator 20 includes an input terminal VIN, an outputterminal VOUT, and a feedback terminal FB. The input terminal VIN isconnected to the standby power supply 5V_SB and grounded via thecapacitor C2. The output terminal VOUT is grounded via the capacitor C3and grounded via the resistors R3 and R4 in series. The feedbackterminal FB is connected to a node between the resistors R3 and R4. Theoutput terminal VOUT outputs the standby power supply 3.3V_SB.

In use, when the motherboard 10 is operating normally, namely the powergood signal PWR_OK received by the gate of the MOSFET Q1 is at highvoltage level and all the power supplies of the motherboard 10respectively achieve the standard voltages, the MOSFET Q1 is turned on,the drain of the MOSFET Q1 outputs a low voltage, thereby the gate ofthe MOSFET Q2 is at low voltage level, the MOSFET Q2 is turned off, thedrain of the MOSFET Q2 outputs a high voltage, the MOSFET Q3 is turnedoff, the MOSFET Q4 is turned on, and the source of the MOSFET Q4provides power to the graphic card 12.

When the motherboard 10 of the computer is suspended, the power goodsignal PWR_OK is at low voltage level. The MOSFET Q1 is turned off, thedrain of the MOSFET Q1 outputs a high voltage, such that the gate of theMOSFET Q2 is at high voltage level, the MOSFET Q2 is turned on, thedrain of the MOSFET Q2 outputs a low voltage, the MOSFET Q3 is turnedon, the MOSFET Q4 is turned off, and the source of the MOSFET Q3provides power to the graphic card 12.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present disclosure have been setforth in the foregoing description, together with details of thestructure and function of the disclosure, the disclosure is illustrativeonly, and changes may be made in details, especially in matters ofshape, size, and arrangement of parts within the principles of thedisclosure to the full extent indicated by the broad general meaning ofthe terms in which the appended claims are expressed.

1. A power supply circuit for a graphic card on a motherboard, the powersupply circuit comprising: a first electrical switch comprising first tothird terminals, wherein the first terminal is operable to receive apower good signal from the motherboard, the second terminal is connectedto a standby power supply via a first resistor, and the third terminalis grounded; a second electrical switch comprising first to thirdterminals, wherein the first terminal is connected to the secondterminal of the first electrical switch, the second terminal isconnected to a first power supply via a second resistor, and the thirdterminal is grounded; a third electrical switch comprising first tothird terminals, wherein the first terminal is connected to the secondterminal of the second electrical switch, and the second terminal isconnected to the standby power supply; and a fourth electrical switchcomprising first to third terminals, wherein the first terminal isconnected to the second terminal of the second electrical switch, thesecond terminal is connected to a second power supply, and the thirdterminal is connected to the third terminal of the third electricalswitch; wherein the second and third terminals of each of the first,second, and fourth electrical switches are connected when the firstterminal of the corresponding electrical switch is at high voltagelevel; the second and third terminals of the third electrical switch areconnected when the first terminal of the third electrical switch is atlow voltage level; the first and second power supplies output highvoltages when the power good signal is at high voltage level, thestandby power supply outputs a high voltage all the time.
 2. The powersupply circuit of claim 1, wherein the third terminals of the third andfourth electrical switches are grounded via at least one capacitor. 3.The power supply circuit of claim 2, wherein the first, second, andfourth electrical switches are n-channel enhancedmetal-oxide-semiconductor field-effect transistors (MOSFETs), the thirdelectrical switch is a p-channel enhanced MOSFET, and the first to thirdterminals of each of the first to fourth electrical switches correspondto a gate, a drain, and a source.
 4. The power supply circuit of claim1, wherein the voltage values of the first power supply, the secondpower supply, and the standby power supply are respectively 12 volts(V), 3.3V, and 3.3V.